US6507648B1 - Method and apparatus for prioritizing voice and data in a circuit-switched network - Google Patents

Abstract

The invention is a novel method of processing incoming and outgoing call requests by a switching unit such as a KSU, PBX or PC server. Each established circuit and each call request is associated with a priority. For an outgoing call request, if an available external bandwidth channel of the appropriate type is found, then a circuit is established at once. However, if there is no available external bandwidth channel of the appropriate type, then the priority of the outgoing call request is checked against the priority of the established circuits. If a lower-priority circuit is found, then that circuit is torn down and a new circuit is established between the internal bandwidth channel carrying the outgoing call request and the external bandwidth channel formerly occupying the established circuit that was torn down. In the case of an incoming call request, a destination terminal device and associated internal bandwidth channels will be specified and availability thereof is verified. If all the bandwidth channels are occupied and if the incoming call request has a higher priority than at least one established circuit involving the destination terminal device, then the existing circuit is torn down and a new one is established between that internal bandwidth channel and the external bandwidth channel carrying the incoming call request.

Description

FIELD OF THE INVENTION

The present invention relates to switching units for use in circuit-switched networks and particularly to the processing of incoming and outgoing call requests of varying priorities at a switching unit.

BACKGROUND OF THE INVENTION

In the majority of business establishments connected to a public or private switched telephone network, the number of potential users of data and telephony services is usually greater than the number of available external interfaces to the network. To manage the allocation of bandwidth on the external interfaces (e.g., external telephone lines) to internal users, businesses usually rely on the use of a switching unit such as a private branch exchange (PBX) or a key system unit (KSU).

The heart of a PBX or KSU is a switch matrix for establishing one-to-one connections between a plurality of bandwidth channels on a number of external lines and, usually, an even greater plurality of bandwidth channels on a number of internal lines. In some cases, internal lines are directly connected to individual terminal devices such as digital telephones, personal computers and point-of-sale terminal adapters (e.g., credit card readers). In other cases, an internal line may be connected to a more sophisticated piece of equipment, such as an Ethernet router/hub or a dialup network terminal adapter, which may be capable of carrying a plurality of bandwidth channels to several of the just mentioned terminal devices.

Generally, the type of connection established between a terminal device and the external network through the switching unit is classifiable as being either a voice or a data connection. A voice connection is usually bidirectional and typically requires the establishment and continuous occupancy of a single circuit joining a bandwidth channel on an external line to a bandwidth channel on the internal line corresponding to the terminal device placing or receiving the call.

On the other hand, a data connection often consists of spurious, unidirectional exchanges of packets which occasionally requires the establishment of additional circuits or the removal of unused ones. Although there is a clear dichotomy between the constant bandwidth requirements of voice and the variable bandwidth requirements of packet-based data communications, both types of information must share the same amount of external network bandwidth available to the switching unit.

Moreover, it is recognized that real-time exchanges such as telephone conversations will generally have a higher priority than store-and-forward data transactions, e.g., E-mail messages. Thus, the nature and priority of a call (or call request) must be taken into account by any system which is to allow voice and data circuits to efficiently and equitably share the same “pool” of bandwidth channels carried by the external lines.

Currently, the most common form of bandwidth management uses line pool servers for allocating a fixed number of external bandwidth channels to voice and a fixed number of external bandwidth channels to data. While this allows a certain minimum number of connections (i.e., circuits) to be established for either type of information exchange, there will always exist conditions under which the fixed allocation will prove inefficient, either because unused data bandwidth channels are not being used for voice or because unused voice bandwidth channels are not being employed for data.

Furthermore, even when the available bandwidth channels carried by the external lines are allocated in a dynamic fashion by the line pool server, switching units employing this technique remain at a disadvantage when faced with a shortage of available bandwidth channels, since the line pool server is not designed to take into account the relative priorities of existing calls and newly made call requests. Clearly, such switching units suffer from being unable to tear down lower-priority connections in order to establish higher-priority connections in their stead.

SUMMARY OF THE INVENTION

It is an object of the present invention to mitigate or obviate one or more disadvantages of the prior art.

Therefore, the invention may be summarized according to a first broad aspect as a switching unit connectable to a plurality of external lines carrying a plurality of external bandwidth channels and also connectable to a plurality of internal lines carrying a plurality of internal bandwidth channels, the switch comprising: a plurality of internal interface units connectable to the internal lines, for receiving outgoing call requests associated with respective internal bandwidth channels; a control unit connected to the internal interface units, for receiving outgoing call requests from the internal interface units and generating respective updated circuit mappings therefrom; and a switch connected to the control unit and to the internal interface units and connectable to the external lines, for controllably establishing circuits between the external bandwidth channels and respective ones of the internal bandwidth channels in accordance with updated circuit mappings received from the control unit; wherein the control unit comprises means for, upon receiving an outgoing call request, determining whether there is an available external bandwidth channel and if so: generating an updated circuit mapping sent to the switch for establishing a circuit between the available external bandwidth channel and the internal bandwidth channel associated with said outgoing call request; otherwise: determining whether the outgoing call request has a higher priority than at least one currently established circuit and if so, generating an updated circuit mapping sent to the switch for interrupting a lower-priority circuit and establishing a new circuit between the external bandwidth channel formerly associated with the interrupted circuit and the internal bandwidth channel associated with said outgoing call request.

In a switching unit comprising a switch for controllably establishing circuits between a plurality of external bandwidth channels and respective ones of a plurality of internal bandwidth channels, the invention may be summarized according to a second broad aspect as a method of processing an outgoing call request associated with an internal bandwidth channel, said outgoing call request having a priority, the method comprising the steps of: determining whether there is an available external bandwidth channel and if so: establishing a circuit between the available external bandwidth channel and the internal bandwidth channel associated with said outgoing call request; otherwise: determining whether the outgoing call request has a higher priority than at least one currently established circuit and if so, interrupting a lower-priority circuit and establishing a new circuit between the external bandwidth channel formerly associated with the interrupted circuit and the internal bandwidth channel associated with said outgoing call request..

The invention may be summarized according to a third broad aspect as a computer-readable storage medium containing software which, when running on a processor in a switching unit for controllably establishing circuits between a plurality of external bandwidth channels and respective ones of a plurality of internal bandwidth channels, follows a sequence of steps to process an outgoing call request associate with an internal bandwidth channel and having a priority, the steps comprising: determining whether there is an available external bandwidth channel and if so: establishing a circuit between the available external bandwidth channel and the internal bandwidth channel associated with said outgoing call request; otherwise: determining whether the outgoing call request has a higher priority than at least one currently established circuit and if so, interrupting a lower-priority circuit and establishing a new circuit between the external bandwidth channel formerly associated with the interrupted circuit and the internal bandwidth channel associated with said outgoing call request.

According to a further broad aspect, the invention may be summarized as a switching unit connectable to at least one external line carrying a plurality external bandwidth channels and also connectable to at least one internal line carrying a plurality of internal bandwidth channels, the internal lines connected to terminal devices, the terminal devices associated with at least one of the plurality of internal bandwidth channels, the switch comprising: a plurality of external interface units connectable to the external lines, for receiving incoming call requests associated with the external bandwidth channels carried by the external lines; a control unit connected to the external interface units, for receiving incoming call requests from the external interface units and generating respective updated circuit mappings therefrom; and a switch connected to the control unit and to the external interface units and connectable to the internal lines, for controllably establishing circuits between the external bandwidth channels and respective ones of the internal bandwidth channels in accordance with updated circuit mappings received from the control unit; wherein the control unit comprises means for, upon receiving an incoming call request from an external interface unit, determining the destination terminal device and determining whether there is at least one available internal bandwidth channel associated with the destination terminal device and if so: if the external bandwidth channel carrying said incoming call request is available, generating an updated circuit mapping sent to the switch for establishing a circuit between an available internal bandwidth channel and the external bandwidth channel associated with said incoming call request; otherwise: determining whether the incoming call request has a higher priority than at least one circuit currently established with the destination terminal device and if so and also if the external bandwidth channel carrying said incoming call request is available, generating an updated circuit mapping sent to the switch for interrupting a lower-priority circuit occupying an internal bandwidth channel associated with the destination terminal device and establishing a new circuit between the internal bandwidth channel formerly associated with the interrupted circuit and the external bandwidth channel associated with said incoming call request.

In a switching unit comprising a switch for controllably establishing circuits between a plurality of external bandwidth channels and respective ones of a plurality of internal bandwidth channels, the invention may be summarized according to yet another broad aspect as a method of processing an incoming call request associated with an the external bandwidth channels, said incoming call request having a priority and associated with a destination terminal device and at least one internal bandwidth channel, the method comprising the steps of: determining whether there is at least one available internal bandwidth channel associated with the destination terminal device and if so: determining whether the external bandwidth channel carrying said incoming call request is available and if so, generating an updated circuit mapping sent to the switch for establishing a circuit between an available internal bandwidth channel and the external bandwidth channel associated with said incoming call request; otherwise: determining whether the incoming call request has a higher priority than at least one circuit currently established with the destination terminal device and if so, determining whether the external bandwidth channel carrying said incoming call request is available and if so, generating an updated circuit mapping sent to the switch for interrupting a lower-priority circuit occupying an internal bandwidth channel associated with the destination terminal device and establishing a new circuit between the internal bandwidth channel formerly associated with the interrupted circuit and the external bandwidth channel associated with said incoming call request.

The invention may be summarized according to still another broad aspect as a computer-readable storage medium containing software which, when running on a processor in a switching unit for controllably establishing circuits between a plurality of external bandwidth channels and respective ones of a plurality of internal bandwidth channels, follows a sequence of steps to process an incoming call request having a priority, the steps comprising: determining whether there is at least one available internal bandwidth channel associated with the destination terminal device and if so: determining whether the external bandwidth channel carrying said incoming call request is available and if so, generating an updated circuit mapping sent to the switch for establishing a circuit between an available internal bandwidth channel and the external bandwidth channel on which said incoming call request was received; otherwise: determining whether the incoming call request has a higher priority than at least one circuit currently established with the destination terminal device and if so, determining whether the external bandwidth channel carrying said incoming call request is available and if so, generating an updated circuit mapping sent to the switch for interrupting a lower-priority circuit occupying an internal bandwidth channel associated with the destination terminal device and establishing a new circuit between the internal bandwidth channel formerly associated with the interrupted circuit and the external bandwidth channel carrying said incoming call request.

BRIEF DESCRIPTION OF THE DRAWINGS

The preferred embodiment of the present invention will now be described with reference to the following figures, in which:

FIG. 1 is a block diagram of a switching unit in accordance with the present invention;

FIG. 2 is a flowchart illustrating an inventive procedure for processing an outgoing call request, as executed by the switching unit of FIG. 1;

FIG. 3 is a flowchart illustrating an inventive procedure for processing an incoming call request, as executed by the switching unit of FIG. 1 when the external bandwidth channel associated with the call request is available;

FIG. 4 is a flowchart illustrating an inventive procedure for processing an incoming call request, as executed by the switching unit of FIG. 1 when the external bandwidth channel associated with the call request is occupied; and

FIG. 5 shows the preferred arrangement of a table used to store information related to circuits established by the switching unit of FIG.1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

With reference to FIG. 1, there is shown in schematic form aswitching unit2 in accordance with the present invention, for establishing circuits between a total of 26 “external” bandwidth channels carried on externalphysical lines4,6,8,10 and a total of 36 “internal” bandwidth channels carried on internalphysical lines12,14,16,18. As a matter of convention, information travelling from the external physical lines to the internal physical lines through theswitching unit2 is hereinafter said to travel in the “downstream” direction, while information flowing in the opposite direction is said to travel in the “upstream” direction.

The term “physical” is used throughout in order to distinguish the external and internal physical lines from logical interconnections. It should be understood that the communications medium used by the external and internal physical lines may consist of copper wire, coaxial cable or optical fiber or a line may be established using a wireless radio link.

The number of external and internal bandwidth channels and physical lines accommodated by the example switching unit in FIG. 1 has been chosen merely to emphasize the need for a switching unit and it should be apparent to those skilled in the art that the present invention is generally applicable to any number of external or internal bandwidth channels or physical lines. Depending on the actual number of bandwidth channels, the switching unit may be categorized as a key system unit (KSU) or as a private branch exchange (PBX). The switching unit could also be a personal computer or a PC or network server that provides switching functionality.

Externalphysical lines4,6,8,10 interface with a switchednetwork20, which may be the public switched telephone network (PSTN), a private network or a combination thereof. The switched network could also include IP based trunks which could be provided by an Internet Service Provider (ISP) or which may form part of a private network or a public IP network. Externalphysical line4, which is known in the art as an analog “trunk”, carries eight analog “plain old telephone service” (POTS) bandwidth channels, external physical line6 carries eight ISDN primary rate (ISDN-PR) digital bandwidth channels, externalphysical line8 carries two ISDN basic rate (ISDN-BR) bandwidth channels and externalphysical line10 carries eight so-called “T1” bandwidth channels.

FIG. 1 also illustrates various candidate devices which may terminate the internalphysical lines12,14,16,18. For instance, internalphysical line12 is shown connected directly to adigital telephone28 for exchanging voice information using a single internal bandwidth channel. Similarly, internalphysical line14 carries packets of data on a single internal bandwidth channel to and from acomputing device30.

Other devices which are physically connected to theswitching unit2 take up more than one internal bandwidth channel. For example, thirty-two internal bandwidth channels are taken up by an integrated router/hub32 connected to theswitching unit2 by internalphysical line16, in this case a fiber optic cable. An example of a router/hub32 is Nortel's IDM200, which communicates with a plurality of personal computers34, digital telephones (not shown) and/or point-of-sale terminal adapters36 elsewhere in the business establishment via an appropriate protocol such as Ethernet.

FIG. 1 further shows theswitching unit2 connected via physicalinternal line18 to anetwork terminal adapter38, such as Nortel's CTA500, which takes up two internal bandwidth channels and dynamically allocates them between apersonal computer40 and adigital telephone42. This type of device gives the end user a choice of using both bandwidth channels for a high-speed data transfer or to use one of them as a digital telephone (voice) connection and the other as a network connection.

Within theswitching unit2, internalphysical line12 is intercepted by aninterface unit46 connected to theswitch matrix44 via an intermediateinternal line48 and also connected to astation emulator50.Interface unit46 comprises circuitry for suitably formatting the upstream signal on internalphysical line12 so as to render the emergent upstream signal on intermediateinternal line48 acceptable to theswitch matrix44.Station interface unit46 also comprises circuitry for decoding (but not necessarily interpreting) an outgoing call request contained in the upstream signal transmitted by thedigital telephone28 over internalphysical line12 and for sending the decoded outgoing call request to thestation emulator50. In addition,interface unit46 comprises circuitry for receiving control messages from thestation emulator50 and for accordingly formatting the downstream signal on intermediateinternal line48 so that the emergent downstream signal on internalphysical line12 adheres to the protocol used by thedigital telephone28.

Asimilar interface unit52 intercepts internalphysical line14 connected to thecomputing device30.Interface unit52 is connected to theswitch matrix44 via an intermediateinternal line54 and is also connected to astation emulator56.Interface unit52 also comprises circuitry for upstream and downstream formatting, in addition to circuitry for decoding an outgoing call request and sending it tostation emulator56, which is similar tostation emulator46. Indeed all the emulators to be described are similar in that they are preferably software entities having a memory and executing a series of instructions either on a respective dedicated processing unit or on a common processor in theswitching unit2.

Internalphysical line16, connected at one end to the router/hub32, is connected at theswitching unit2 to aninterface unit58, itself connected to theswitch matrix44 via an intermediateinternal line60. Since the signal exchanged between theswitching unit2 and the router/hub32 is optical in nature,interface unit58 comprises circuitry for conversion of this signal from optical to electronic form (or vice versa), under control of a router/hub emulator62 to which it is connected by a control line.

In addition, since the router/hub32 is a relatively complex entity handling a large number of internal bandwidth channels, it may be necessary forinterface unit58 to comprise circuitry for supporting an additional optical control channel allowing the exchange of control parameters with the router/hub32, such control parameters being interpreted and generated by router/hub emulator62. The optical control channel may encapsulate outgoing call requests made by the terminal devices connected to the router/hub32. The optical control channel may take up one or more of the internal bandwidth channels exchanged between theswitching unit2 and the router/hub32.

Internalphysical line18, which is connected at one end to thenetwork terminal adapter38, is intercepted at theswitching unit2 by aninterface unit64 which is connected to theswitch matrix44 via an intermediateinternal line66.Interface unit64 comprises circuitry for conditioning the upstream signal arriving on internalphysical line18 so as to provide an upstream signal on intermediateinternal line66 in a format accepted by theswitch matrix44.

In addition,interface unit64 comprises circuitry for formatting the downstream signal arriving on intermediateinternal line66 so as to render the emergent downstream signal on internalphysical line18 acceptable to thenetwork terminal adapter38. Furthermore,interface unit64 is connected to anadapter emulator68 and also comprises decoding circuitry for decoding an outgoing call request generated by the devices connected to thenetwork terminal adapter38 and relayed by the latter to theadapter emulator68.

External lines4,6,8,10 are similarly connected to theswitching unit2 by corresponding interface units, which are also connected to the switch matrix and to corresponding emulators. Specifically, external physical line (or trunk)4 is connected at the switching unit to aninterface unit70, which is connected to theswitch matrix44 via an intermediateexternal trunk72.

Interface unit70 comprises circuitry for formatting the analog upstream POTS signals onexternal trunk4 into a digital format supported by theswitch matrix44 and vice versa. Formatting control is executed by atrunk emulator74 connected to interfaceunit70. Interface unit also comprises circuitry for decoding an incoming call request (which it sends totrunk emulator74 for further processing) and for generation of a busy signal under control oftrunk emulator74.

Externalphysical lines6 and8 are connected to separate ports of a commonISDN interface unit76, which is then connected to theswitch matrix44 via an intermediateexternal line78 carrying all10 ISDN-type external bandwidth channels.Interface unit76 is connected to anISDN emulator80 and comprises formatting circuitry in addition to circuitry for decoding an incoming call request associated with one of the external bandwidth channels carried by externalphysical lines6,8 and communicating the call request 'toISDN emulator80. The incoming call requests usually arrive on a separate control channel (not included among the8 primary rate and2 basic rate bandwidth channels).Interface unit76 also comprises circuitry for communicating control information with other elements in the switchednetwork20 via externalphysical lines6,8.

Externalphysical line10 carrying Ti traffic on8 external bandwidth channels is intercepted at theswitching unit2 by aninterface unit82, which is connected to theswitch matrix44 by an intermediateexternal line84.Interface unit82 comprises formatting circuitry as well as circuitry for decoding incoming call requests arriving on externalphysical line10.Interface unit82 is also connected to aT1 emulator86, from which it derives formatting instructions and to which it provides decoded incoming call requests.

Theswitching unit2 also comprises acontrol unit92, preferably a micro-processor, a micro-controller or other type of programmable logic device, which is connected to theemulators50,56,62,68,74,80,86, preferably via a software orhardware bus90. Thecontrol unit92 may occupy the same processor as theemulators50,56,62,68,74,80,86. Thecontrol unit92 is also connected to theswitch matrix44, preferably using adedicated hardware link94, although theswitch matrix44 is also implementable in software in which case link94 would represent the exchange of software parameters between thecontrol unit92 and theswitch matrix44.

It is to be noted that outgoing call requests which are present in the signals carried on internalphysical lines12,14,16,18 and incoming call requests which are present in the signals carried on externalphysical lines4,6,8,10 are captured by the corresponding interface units and emulators and therefore may not appear on the signals travelling on the corresponding intermediate lines. Nevertheless, the information content (e.g., voice or data) remains unaltered as it travels through the switching unit in either direction.

In operation, thecontrol unit92 receives parameters related to incoming and outgoing call requests from the various emulators, processes them and provides theswitch matrix44 with a dynamic circuit mapping for establishing one-to-one connections (i.e., circuits) between the various external and internal bandwidth channels. Each of three distinct scenarios is now discussed in further detail.

Outgoing Call Request

The first scenario is one in which an outgoing call request is made by an originating terminal device and arrives at theswitching unit2 via the internal bandwidth channel corresponding to the originating terminal device. Reference is made to FIG. 2, which shows a sequence steps executed by the emulators and the control unit within the switching unit when handling outgoing call requests received by a digital telephone, computer terminal or other “originating terminal device” connected either directly or indirectly to the customer premises end of the switching unit.

STEP202:

If the originating terminal device is connected directly to theswitching unit2, as is the case with terminal device28 (or30), then the outgoing call request is detected and decoded by the corresponding interface unit46 (or52), which sends the outgoing call request to the corresponding station emulator50 (or56).

On the other hand, if the originating terminal device interfaces through a multi-channel device, such as router/hub32 ornetwork terminal adapter38, then the multi-channel device itself detects the outgoing call request and relays it to the correspondinginterface unit58 or64 in a suitable format using, e.g., a control channel. The interface unit58 (or64) then decodes the outgoing call request and sends it to the corresponding emulator62 (or68).

A decoded outgoing call request comprises information relating to the priority of the call, which is most commonly an indication of the call type (voice or data), but which may be of a more complex nature. In addition, the outgoing call request may specify a desired “line pool” which indicates the pool of external physical lines, usually grouped according to line type (e.g., POTS analog, ISDN-PR, ISDN-BR, T1 digital, IP trunk) that should be used for establishing a connection in the region between the switching unit and the switchednetwork20.

The emulator receiving the outgoing call request from the originating terminal device then encapsulates the priority information and the desired line pool, if specified, into a message sent onto thebus90 and destined for thecontrol unit92.

STEP206:

Thecontrol unit92, by virtue of being connected to thebus90, subsequently receives the message sent in accordance withstep202 by an emulator and verifies whether an external bandwidth channel is available. If, in addition, a desired line pool is specified, then only those bandwidth channels carried by external lines within that pool (i.e., of the appropriate type) are searched for an available bandwidth channel.

Searching for an available external bandwidth channel can be done by thecontrol unit92 consulting a table stored in local memory, although it is to be understood that considerably more sophisticated algorithms could be used for this purpose. Nevertheless, the use of a table is assumed hereinbelow for the sake of simplicity. Furthermore, assuming the external and internal bandwidth channel configuration of FIG. 1 this table may have the form shown in FIG.5.

With reference to FIG. 5, each row in the table has a plurality of fields, including an “external line pool”field520, an “external bandwidth channel”field530, an “internal bandwidth channel”field540 and a “call priority”field540. The number of rows corresponds to the total number of external bandwidth channels and therefore in the case of the arrangement of FIG. 1, the corresponding table would have twenty-six rows.

In a given row, the “external bandwidth channel”field530 identifies the corresponding external bandwidth channel by means of, e.g., a number, while the “external line pool”field520 indicates the type of external physical line associated with that external bandwidth channel and is meaningful only when the desired line pool accompanies an outgoing call request. In general, the “external bandwidth channel”field530 and the “external line pool”field520 can be fixed, although they would be modified for different switchednetworks20 interfacing with theswitching unit2.

When a circuit is established between an external bandwidth channel and internal bandwidth channel, then an identification of the internal bandwidth channel is inserted into the “internal bandwidth channel”field540 of the row corresponding to the external bandwidth channel. Finally, the “call priority”field550, which is valid for a given row of the table only when a circuit is in existence between the corresponding external bandwidth channel and a certain internal bandwidth channel, indicates the priority of the circuit thereby established.

Therefore, upon consulting a table of the form shown in FIG. 5, it is possible for thecontrol unit92 to determine whether or not an external bandwidth channel is available (in the desired line pool, when specified) simply by verifying occupancy of the “internal bandwidth channel” field in each row of the table. If thecontrol unit92 indeed finds an available external bandwidth channel, then this external bandwidth channel is identified andpath206A is followed to STEP208; otherwisepath206B is followed toSTEP214.

STEP208:

In this case, a circuit can be established between the internal bandwidth channel corresponding to the originating terminal device and the available external bandwidth channel identified inSTEP206. Firstly, thecontrol unit92 updates the row corresponding to the available external bandwidth channel by entering an internal bandwidth channel identifier in the “internal bandwidth channel”field540 and by entering the call priority in the “call priority”field550. The inventive procedure then advances to STEP210.

STEP210:

Having updated its internal table, thecontrol unit92 sends a message to theswitch matrix44 via thededicated link94, containing an updated circuit mapping for theswitch matrix44. The updated circuit mapping need not comprise all the elements of the locally stored table. For example, when a new circuit is established, only the participating external and internal bandwidth channels need be specified to theswitch matrix44. (In addition, as will be seen later, theswitch matrix44 may be forced to interrupt an existing circuit, in which case thecontrol unit92 would specify the external and internal bandwidth channels corresponding to the circuit that is to be torn down.)

Theswitch matrix44 then receives the updated circuit mapping and establishes (and, if applicable, interrupts) the circuit(s) as specified in the updated circuit mapping.

STEP212:

After theswitch matrix44 establishes (and, if applicable, tears down) the circuit(s) specified in the updated circuit mapping, thecontrol unit92 sends an acceptance message out onto thebus90. This message identifies the internal and external bandwidth channels that form the newly established circuit and, if applicable, those formerly comprising a circuit that has been torn down. The acceptance message is destined for the emulator associated with the originating terminal device as well as for the emulator associated with the external line carrying the now occupied (formerly available) external bandwidth channel.

The emulator associated with the now occupied external bandwidth channel receives the acceptance message and, in the case of an ISDN bandwidth channel, the emulator reacts by appending control information such as the call priority to the ISDN primary or basic rate signal leaving theswitching unit2 and headed for the switchednetwork20.

The emulator associated with the internal bandwidth channel corresponding to the originating terminal device also receives the acceptance message and if the originating terminal device is separated from theswitching unit2 by an intermediate multi-channel device (such as router/hub32 or network terminal adapter38), then the emulator notifies the intermediate device of successful call placement via the respective interface unit (58 or64). The router/hub32 ornetwork terminal adapter38 itself then performs the necessary remaining operations in order to allow the originating terminal device to begin communicating information through the switching unit.

STEP214:

It is recalled that this step is entered when no external bandwidth channel (in the desired line pool, when specified) is available. In this case, thecontrol unit92 must verify whether or not the outgoing call request has a higher priority than any one of the calls currently in progress and occupying the external bandwidth channels (in the desired line pool, when specified). When using a locally stored table as previously described, this can be achieved by comparing the call priority of the outgoing call request with the “call priority” field in each row of the table.

If it is found that the outgoing call request has a higher priority than at least one of the calls currently in progress, then STEP218 is to be followed; otherwise the inventive method proceeds withSTEP216.

STEP216:

Because the outgoing call request has a lower priority, the request is denied, and this is indicated by thecontrol unit92 sending a denial message on thebus90 which is received by the emulator associated with the originating terminal device. The emulator will either command the corresponding interface unit to send a connection rejection or connection denial signal (e.g. a busy signal) to the originating terminal device or, if the emulator is connected to an intermediate device (e.g., router/hub32 or adapter38), it will indicate to the intermediate device that the requested call cannot be placed, resulting in termination of the inventive procedure.

STEP218:

This step consists of thecontrol unit92 locating an established circuit that can be torn down in order to allow placement of the requested call. There are various ways of selecting the circuit to be torn down, of which three are now discussed. First, thecontrol unit92 itself may make the decision as to which circuit is to be torn down. If an internally stored table such as that in FIG. 5 is employed, then the circuit to be torn down is chosen in accordance with the lowest value in the “call priority” field among all rows. Alternatively, a “least-used” or “last-used” algorithm can be implemented by thecontrol unit92.

While this first, centralized approach is simple and effective, it is not necessarily efficient when there are existing circuits established with terminal devices connected to the switching unit via intermediate multi-channel devices (e.g., router/hub32 or network terminal adapter38). In this case, a second method may be used, whereby thecontrol unit92 instructs the intermediate device (via the associated emulator and interface unit) to drop one of its existing connections. This allows the intermediate device to intelligently designate the connection to be dropped, which might be capable of mitigating the effects of a reduction in bandwidth available to other, currently occupied terminal devices.

However, in the event that a satisfactory selection cannot be made, the intermediate device would nevertheless be forced to select a circuit that will be interrupted. The third option therefore consists of the corresponding emulator asking the intermediate device whether it is capable of dropping a circuit without adversely affecting system performance. If the third approach is taken, then the intermediate device would require modifications in order to enable it to accept the query from the emulator in the switching unit, to process the query and to respond to it.

In any event, once thecontrol unit92 determines the external bandwidth channel corresponding to the circuit which is to be torn down. This external bandwidth channel is deemed “available” and the inventive method executesSTEP208,STEP210 andSTEP212 in the manner described above.

Incoming Call Request—External Bandwidth Channel Available

Also within the scope of the present invention is the processing of “incoming” call requests received from the switchednetwork20 on the bandwidth channels carried byexternal lines4,6,8,10, each such call request identifying a destination terminal device.

Reference is now made to FIG. 3, which reveals the steps in an inventive bandwidth management procedure executed by the emulators and control unit within the switching unit each time an incoming call request identifying a destination terminal device is received from the switchednetwork20 on one of the external bandwidth channels when such bandwidth channel is free (i.e., unoccupied).

STEP300:

An incoming call request arriving on an external bandwidth channel is decoded by the corresponding interface unit and sent to the corresponding emulator, which then relays the incoming call request onto thebus90.

STEP304:

Thecontrol unit92, being connected to thebus90, subsequently receives the message sent inSTEP300, determines the priority of the incoming call request and verifies whether an internal bandwidth channel corresponding to the destination terminal device is free. If a table such as that shown in FIG. 5 is used, then occupancy of the internal bandwidth channels can be determined by checking for the presence of the internal bandwidth channel identifiers associated with the destination terminal device in the “internal bandwidth channel” field for some row in the table.

If thecontrol unit92 finds that one or more internal bandwidth channels corresponding to the destination terminal device are free, thenpath304A is followed to STEP306; otherwisepath304B is followed toSTEP312.

STEP306:

At this stage, a circuit can be established immediately between the external bandwidth channel carrying the incoming call request and an internal bandwidth channel associated with the destination terminal device. Thecontrol unit92 stores the identifier of the chosen internal bandwidth channel in the “internal bandwidth channel” field of the row corresponding to the external bandwidth channel providing the incoming call request. The priority of the incoming call request, soon to become an established circuit, is entered in the “call priority” field of the corresponding row and the inventive procedure advances to STEP308.

STEP308:

Having updated its locally stored table, thecontrol unit92 sends a message to theswitch matrix44 via thededicated link94, the message containing an updated circuit mapping for theswitch matrix44. The updated circuit mapping specifies the internal and external bandwidth channels of the circuit to be established. (As will be shown later, the updated circuit mapping may also specify a circuit to be torn down.) Upon receipt of the updated mapping, theswitch matrix44 establishes (and possibly interrupts) the specified circuit or circuits. The inventive procedure continues withSTEP310.

STEP310:

After theswitch matrix44 establishes (and possibly interrupts) the specified circuit(s), thecontrol unit92 sends an acceptance message onto thebus90 destined for the emulator associated with the external bandwidth channel providing the incoming call request. This message contains an indication that the call request has been accepted, i.e., that a circuit between the internal bandwidth channel corresponding to the destination terminal device and the external bandwidth channel providing the incoming call request has been successfully established.

With reference to FIG. 1, if the destination terminal device is connected to interfaceunit46 or52, then upon receipt of the acceptance message, the corresponding station emulator (50 or56) will send a message to the interface unit instructing it to provide a call indication signal on the bandwidth channel corresponding to the destination terminal device.

However, if the destination terminal device is25 separated from the switching unit by an intermediate multi-channel device (such as the router/hub32 or adapter38), then the corresponding emulator notifies the intermediate device of successful call placement via the respective interface unit. It is then up to the intermediate device itself to perform any remaining operations in order to allow the destination terminal device to communicate information through the switching unit.

The emulator associated with the external bandwidth channel that provides the incoming call request may, in the case of ISDN, append an indication of successful call placement to the ISDN primary or basic rate signal leaving theswitching unit2 and headed for the switchednetwork20.

STEP312:

Recalling that this step is executed when it is determined that all the internal bandwidth channels corresponding to the destination terminal device are occupied, thecontrol unit92 must verify whether or not the incoming call request has a higher priority than any call that has already been established with the destination terminal device. If a table such as that shown in FIG. 5 is used, then the priority of the incoming call request is compared to the value in the “call priority” field of the row corresponding to the external bandwidth channel(s) forming part of a circuit with the destination terminal device.

If it is found that the requested call has a higher priority than any of the circuits currently engaging the destination terminal device, then STEP316 is followed. However, in the case of the incoming call request having a lower priority than one of the current calls in progress,STEP314 is to be followed.

STEP314:

The incoming call request is denied, as indicated by a message sent on thebus90 by thecontrol unit92. This message is received by the emulator associated with the external bandwidth channel providing the incoming call request, which will order the corresponding interface unit to send a connection rejection or connection denial signal (e.g., a busy signal) back to the switchednetwork20, thus terminating the inventive procedure for this incoming call request.

STEP316:

This step is essentially identical to step306, except that a current circuit involving the destination terminal device is torn down. This additional stage involves erasing the “internal bandwidth channel” field and the “call priority” field of the row corresponding to the external bandwidth channel formerly communicating with the destination terminal device.

Steps308 and310 are then executed in the manner described above, wherein thecontrol unit92 sends an updated circuit mapping to theswitch matrix44, followed by theswitch matrix44 consequently tearing down an existing circuit and establishing a new one.

Incoming Call Request—External Bandwidth Channel Occupied

The present invention also provides for processing of an incoming call request that arrives on an external bandwidth channels which is occupied. A method of processing such an incoming call request is now described with reference to the flowchart in FIG.4. For the sake of simplicity, it is assumed that only one internal bandwidth channel is associated with each terminal device, although it will be understood that multiple circuits could be established with each device.

STEP400:

An incoming call request arriving on an external bandwidth channel is decoded by the corresponding interface unit and sent to the corresponding emulator, which then relays the incoming call request to onto thebus90.

STEP404:

Thecontrol unit92 receives the message sent inSTEP400, determines the priority of the incoming call request and verifies whether the internal bandwidth channel corresponding to the destination terminal device is free. If a table such as that shown in FIG. 5 is used, then occupancy of the internal bandwidth channel can be determined by checking for the presence of the internal bandwidth channel identifier in the “internal bandwidth channel” field for some row in the table.

If thecontrol unit92 finds that the internal bandwidth channel corresponding to the destination terminal device is free, then the inventive procedure continues withSTEP410; otherwise STEP406 is followed.

STEP406:

Since the internal bandwidth channel is not available, it must be determined whether or not the incoming call request has a higher priority that the circuit which has already been established with the destination terminal device. IF a table such as that shown in FIG. 5 is used, then the priority incoming call request is compared to the value in the “call priority” field of the row corresponding to the external bandwidth channel currently communicating with the destination terminal device.

If it is found that the requested call has a higher priority than the call currently in progress, then STEP410 is followed; otherwise, the call is deniedSTEP408 is followed.

STEP408:

The incoming call request is denied, as indicated by a message sent on thebus90 by thecontrol unit92. This message is received by the emulator associated with the external bandwidth channel providing the incoming call request. which will order the corresponding interface unit to send a connection rejection or connection denial signal (e.g., a busy signal) back to the switchednetwork20, thus terminating the inventive procedure for this incoming call request.

STEP410:

At this stage, thecontrol unit92 determines whether the external bandwidth channel carrying the incoming call request can be liberated. This is done based on the priority of the incoming call request and that of the circuit established with the external bandwidth channel providing the request. If a table such as that shown in FIG. 5 is used, then the “call priority” column will contain the priority information necessary for this comparison operation. If the incoming call request has a higher priority, then STEP412 is followed; otherwise, the call must be denied andSTEP408 is followed in the previously described manner.

STEP412:

The control unit must now tear down either one or two circuits, depending on the result ofSTEP406 andSTEP410, in order to establish the connection between the external bandwidth channel carrying the incoming call request and internal bandwidth channel associated with the destination terminal device.

If a table such as that shown in FIG. 5 is used, then the “internal bandwidth channel” field currently containing the identification of the internal bandwidth channel associated with the destination terminal device is erased and the “internal bandwidth channel” field of the external bandwidth channel providing the incoming call request is filled with the identification of the internal bandwidth channel associated with the destination terminal device.

STEP414:

Having updated its locally stored table, thecontrol unit92 sends a message to theswitch matrix44 via the dedicated link, the message containing an updated circuit mapping for theswitch matrix44. The updated circuit mapping specifies the internal and external bandwidth channels corresponding to the circuit that needs to be torn down and to the circuit that needs to be set up.

STEP416:

After theswitch matrix44 performs the required changes to the mapping, thecontrol unit92 sends an acceptance message onto thebus90 destined for the emulator associated with the external bandwidth channel providing the incoming call request. This message contains an indication that the call request has been accepted and that the former call has been torn down.

It is to be understood that in any case where a circuit has been torn down in favour of establishing a higher priority circuit subsequent to an incoming or outgoing call request, the internal devices which had their lower priority call interrupted may attempt to re-acquire the lost bandwidth on a periodic basis. This can be achieved by placing periodic outgoing call requests at intervals which may be based on a timer value (possibly administrable) which is long enough to allow the new higher priority call to get established.

While the preferred embodiment of the present invention has been described and illustrated, it will be apparent to one skilled in the art that numerous modifications and variations are possible. The scope of the invention is therefore only to be limited by the claims appended hereto.

Claims (22)

We claim:

1. A switching unit connectable to a plurality of external lines carrying a plurality of external bandwidth channels and also connectable to a plurality of internal lines carrying a plurality of internal bandwidth channels, the switch comprising:

a plurality of internal interface units connectable to the internal lines, for receiving outgoing call requests associated with respective internal bandwidth channels;

a control unit connected to the internal interface units, for receiving outgoing call requests from the internal interface units and generating respective updated circuit mappings therefrom; and

a switch connected to the control unit and to the internal interface units and connectable to the external lines, for controllably establishing circuits between the external bandwidth channels and respective ones of the internal bandwidth channels in accordance with updated circuit mappings received from the control unit;

wherein the control unit comprises means for, upon receiving an outgoing call request, determining whether there is an available external bandwidth channel and

if so: generating an updated circuit mapping sent to the switch for establishing a circuit between the available external bandwidth channel and the internal bandwidth channel associated with said outgoing call request;

otherwise: determining whether the outgoing call request has a higher priority than at least one currently established circuit and if so, generating an updated circuit mapping sent to the switch for interrupting a lower-priority circuit and establishing a new circuit between the external bandwidth channel formerly associated with the interrupted circuit and the internal bandwidth channel associated with said outgoing call request.

2. A switching unit according toclaim 1, wherein the switch is a digital switch matrix.

3. A switching unit according toclaim 1, wherein the internal interface units comprise circuitry for formatting signals leaving or entering the switching unit on the internal lines.

4. A switching unit according toclaim 1, further comprising a plurality of external interface units connectable to the external lines and connected to the control unit and to the switch, for formatting the signals leaving or entering the switching unit on the external lines.

5. A switching unit according toclaim 1, further comprising a plurality of emulators connected between the control unit and respective internal interface units, wherein each emulator comprises means for receiving and processing an outgoing call request from the respective internal interface, thereby to extract the priority of the outgoing call request.

6. A switching unit according toclaim 5, wherein the control unit and emulators are interconnected in a hardware bus architecture.

7. A switching unit according toclaim 5, wherein the control unit and emulators are implemented in software and communicate through the exchange software parameters.

8. A switching unit according toclaim 1, wherein the control unit communicates with the switch using a dedicated hardware link.

9. A switching unit according toclaim 6, wherein the switch is also interconnected via the hardware bus architecture.

10. A switching unit according toclaim 7, wherein the switch is also implemented in software and communicates via the exchange of software parameters.

11. A switching unit according toclaim 1, wherein the control unit is a processor comprising a table stored in memory, said table containing a record of the external bandwidth channel, the internal bandwidth channel and the priority associated with each established circuit.

12. A switching unit according toclaim 1, wherein the internal bandwidth channels carry a mixture of voice and data traffic.

13. A switching unit according toclaim 12, wherein voice is considered to have a higher priority than data.

14. A switching unit according toclaim 12, wherein data is said to have a higher priority than voice.

15. In a switching unit comprising a switch for controllably establishing circuits between a plurality of external bandwidth channels and respective ones of a plurality of internal bandwidth channels, a method of processing an outgoing call request associated with an internal bandwidth channel, said outgoing call request having a priority, the method comprising the steps of:

determining whether there is an available external bandwidth channel and

if so: establishing a circuit between the available external bandwidth channel and the internal bandwidth channel associated with said outgoing call request;

otherwise: determining whether the outgoing call request has a higher priority than at least one currently established circuit and if so, interrupting a lower-priority circuit and establishing a new circuit between the external bandwidth channel formerly associated with the interrupted circuit and the internal bandwidth channel associated with said outgoing call request.

16. A computer-readable storage medium containing software which, when running on a processor in a switching unit for controllably establishing circuits between a plurality of external bandwidth channels and respective ones of a plurality of internal bandwidth channels, follows a sequence of steps to process an outgoing call request associate with an internal bandwidth channel and having a priority, the steps comprising:

determining whether there is an available external bandwidth channel and

if so: establishing a circuit between the available external bandwidth channel and the internal bandwidth channel associated with said outgoing call request;

otherwise: determining whether the outgoing call request has a higher priority than at least one currently established circuit and if so, interrupting a lower-priority circuit and establishing a new circuit between the external bandwidth channel formerly associated with the interrupted circuit and the internal bandwidth channel associated with said outgoing call request.

17. A switching unit connectable to at least one external line carrying a plurality external bandwidth channels and also connectable to at least one internal line carrying a plurality of internal bandwidth channels, the internal lines connected to terminal devices, the terminal devices associated with at least one of the plurality of internal bandwidth channels, the switch comprising:

a plurality of external interface units connectable to the external lines, for receiving incoming call requests associated with the external bandwidth channels carried by the external lines;

a control unit connected to the external interface units, for receiving incoming call requests from the external interface units and generating respective updated circuit mappings therefrom; and

a switch connected to the control unit and to the external interface units and connectable to the internal lines, for controllably establishing circuits between the external bandwidth channels and respective ones of the internal bandwidth channels in accordance with updated circuit mappings received from the control unit;

wherein the control unit comprises means for, upon receiving an incoming call request from an external interface unit, determining the destination terminal device and determining whether there is at least one available internal bandwidth channel associated with the destination terminal device and

if so: if the external bandwidth channel carrying said incoming call request is available, generating an updated circuit mapping sent to the switch for establishing a circuit between an available internal bandwidth channel and the external bandwidth channel associated with said incoming call request;

otherwise: determining whether the incoming call request has a higher priority than at least one circuit currently established with the destination terminal device and if so and also if the external bandwidth channel carrying said incoming call request is available, generating an updated circuit mapping sent to the switch for interrupting a lower-priority circuit occupying an internal bandwidth channel associated with the destination terminal device and establishing a new circuit between the internal bandwidth channel formerly associated with the interrupted circuit and the external bandwidth channel associated with said incoming call request.

18. A switching unit according toclaim 17, wherein the control unit further comprises means for:

if the external bandwidth channel associated with said incoming call request is occupied, determining whether the incoming call request has a higher priority than the circuit occupying the external bandwidth channel associated with said incoming call request and if not, generating an updated circuit mapping sent to the switch for interrupting a lower-priority circuit occupying an internal bandwidth channel associated with the destination terminal device, interrupting the circuit occupying the external bandwidth channel carrying the incoming call request and establishing a new circuit between the internal bandwidth channel formerly associated with the interrupted lower-priority circuit and the external bandwidth channel associated with said incoming call request.

19. In a switching unit comprising a switch for controllably establishing circuits between a plurality of external bandwidth channels and respective ones of a plurality of internal bandwidth channels, a method of processing an incoming call request associated with an the external bandwidth channels, said incoming call request having a priority and associated with a destination terminal device and at least one internal bandwidth channel, the method comprising the steps of:

determining whether there is at least one available internal bandwidth channel associated with the destination terminal device and

if so: determining whether the external bandwidth channel carrying said incoming call request is available and if so, generating an updated circuit mapping sent to the switch for establishing a circuit between an available internal bandwidth channel and the external bandwidth channel associated with said incoming call request;

otherwise: determining whether the incoming call request has a higher priority than at least one circuit currently established with the destination terminal device and if so, determining whether the external bandwidth channel carrying said incoming call request is available and if so, generating an updated circuit mapping sent to the switch for interrupting a lower-priority circuit occupying an internal bandwidth channel associated with the destination terminal device and establishing a new circuit between the internal bandwidth channel formerly associated with the interrupted circuit and the external bandwidth channel associated with said incoming call request.

20. A method according toclaim 19, further comprising the step of:

if the external bandwidth channel associated with said incoming call request is occupied, the control unit determining whether the incoming call request has a higher priority than the circuit occupying the external bandwidth channel associated with said incoming call request and if not, generating an updated circuit mapping sent to the switch for interrupting a lower-priority circuit occupying an internal bandwidth channel associated with the destination terminal device, interrupting the circuit occupying the external bandwidth channel carrying the incoming call request and establishing a new circuit between the internal bandwidth channel formerly associated with the interrupted lower-priority circuit and the external bandwidth channel associated with said incoming call request.

21. A computer-readable storage medium containing software which, when running on a processor in a switching unit for controllably establishing circuits between a plurality of external bandwidth channels and respective ones of a plurality of internal bandwidth channels, follows a sequence of steps to process an incoming call request having a priority, the steps comprising:

determining whether there is at least one available internal bandwidth channel associated with the destination terminal device and

if so: determining whether the external bandwidth channel carrying said incoming call request is available and if so, generating an updated circuit mapping sent to the switch for establishing a circuit between an available internal bandwidth channel and the external bandwidth channel on which said incoming call request was received;

otherwise: determining whether the incoming call request has a higher priority than at least one circuit currently established with the destination terminal device and if so, determining whether the external bandwidth channel carrying said incoming call request is available and if so, generating an updated circuit mapping sent to the switch for interrupting a lower-priority circuit occupying an internal bandwidth channel associated with the destination terminal device and establishing a new circuit between the internal bandwidth channel formerly associated with the interrupted circuit and the external bandwidth channel carrying said incoming call request.

22. A computer-readable storage medium according toclaim 21, wherein the sequence of steps further comprises the step of:

if the external bandwidth channel associated with said incoming call request is occupied, determining whether the incoming call request has a higher priority than the circuit occupying the external bandwidth channel associated with said incoming call request and if not, generating an updated circuit mapping sent to the switch for interrupting a lower-priority circuit occupying an internal bandwidth channel associated with the destination terminal device, interrupting the circuit occupying the external bandwidth channel carrying the incoming call request and establishing a new circuit between the internal bandwidth channel formerly associated with the interrupted lower-priority circuit and the external bandwidth channel associated with said incoming call request.

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